1. Field of the Invention
This invention relates generally to hypodermic syringes and more particularly to a hypodermic syringe with a needle that may be retracted and locked into a retracted position after use.
2. Description of the Prior Art
Hypodermic syringes are widely used in the medical art. However, in recent years the prevalence of certain types of infectious diseases, such as acquired immune deficiency syndrome and hepatitis have raised concerns regarding the safe use and disposal of hypodermic syringes. Workers in the medical field are well aware that hypodermic syringes are notorious vehicles for the transmission of infectious diseases. If a hypodermic syringe is used on an infected patient, the used syringe becomes a dangerous source of potential infection. Needle pricks are a common hazard to healthcare workers.
In order to overcome this problem, a number of hypodermic syringes have been developed which incorporate means for retracting the needle into the body of the syringe after use so that the risk of contamination by needle prick is substantially reduced thereby allowing the safe disposal of the used syringe.
In order to effect the withdrawal of the used needle into the body of the syringe, the prior art generally shows some means for engaging the needle by the head of the plunger. A large number of variations on this basic concept have been disclosed.
In addition to means for withdrawing the used needle into the body of the syringe, the prior art also discloses a number of syringes having means to lock the needle into a retracted position to prevent reuse. These locking means are generally of two types. One type employs a stop or detent mechanism that permanently locks the plunger into a retracted position within the barrel of the syringe. An example of this type is U.S. Pat. No. 5,026,354 for "Safety Syringe Apparatus" issued to Kocses on Jun. 25, 1991. Another type of locking means involves a mechanism to push the retracted needle to one side, thus making it impossible to reuse the needle after it has been retracted into the body of the syringe. This type of mechanism is disclosed in U.S. Pat. No. 4,986,813 for "Disposable Hypodermic Syringe" issued to Blake, et al. on Jan. 22, 1991.
As an added safety measure some of the prior art discloses means for the plunger to be broken off after withdrawal of the needle into the body of the syringe. Examples of this are found in U.S. Pat. No. 4,790,882 for "Retractable Hypodermic Safety Syringe" issued to Haining on Dec. 13, 1988 and U.S. Pat. No. 4,952,251 for "Simplified Retractable Needle Syringe" issued to Haining on Aug. 21, 1990.
In attempting to find a solution to the problem of a safely disposable retractable needle syringe, the prior art discloses a number of solutions which suffer from their extreme complexity. The prior art retractable needles are often highly complex, at times perhaps, even to the point of being infeasible to manufacture. Furthermore, the prior art retractable needle syringes fail to take into account the need to produce an instrument that is manufacturable and marketable by limiting the alterations to the standard type of manufactured hypodermic syringe to those features absolutely necessary to produce a safe retractable needle syringe. A design of a retractable needle syringe that departs too greatly from the standard design is likely to prove commercially unacceptable.
Furthermore, the prior art has concentrated on the concept of a retractable needle syringe that can only be used one time. Under certain circumstances a multiple-use syringe might be desirable.